Poly(ether amide) dendrimers via nucleophilic ring-opening addition reactions of phenol groups toward oxazolines: Synthesis and characterization

Article abstract of DOI:10.1021/ma034318y

The synthesis of aliphatic-aromatic poly(ether amide) dendrimers via ring-opening addition reaction of phenol groups toward oxazoline up to generation 3 is presented. The first and second generation could be prepared both by convergent and divergent appro

Full text of DOI:10.1021/ma034318y

Macromolecules 2003, 36, 7065-7074
7065
Poly(ether amide) Dendrimers via Nucleophilic Ring-Opening Addition
Reactions of Phenol Groups toward Oxazolines: Synthesis and
Characterization
Ca r ola Cla u sn itzer , Br igitte Voit,* Ha r tm u t Kom ber , a n d Dieter Voigt
Institut fu¨r Polymerforschung Dresden e.V., Hohe Strasse 6, D-01069 Dresden, Germany
Received March 14, 2003; Revised Manuscript Received J uly 6, 2003
ABSTRACT: The synthesis of aliphatic-aromatic poly(ether amide) dendrimers via ring-opening addition
reaction of phenol groups toward oxazoline up to generation 3 is presented. The first and second generation
could be prepared both by convergent and divergent approaches. The ring-opening addition reaction was
carried out in bulk at temperatures between 140 and 190 °C, followed by hydrogenation of the protecting
1
benzyl ether units with palladium catalyst. The dendrons and dendrimers were characterized by H and
13C NMR spectroscopy, MALDI-TOF MS, SEC, and DSC. The synthetic scheme applied allowed to prepare
perfect dendrimers having identical structure and end groups as previously described hyperbranched
polymers which enabled a direct comparison of the properties. Melt rheology measurements on the
dendrimers revealed a predominantly elastic behavior with a relatively high viscosity at low frequency,
as was found also for the hyperbranched analogues. The second generation of one of the poly(ether amide)
dendrimers was mixed with linear polyamide 6 (PA6) in melt up to an amount of 1 wt % in order to
evaluate the influence of dendrimers on the properties of the matrix. The dendrimer was fully miscible
with the matrix, but in contrast to the hyperbranched polymers of higher molar mass, it had no influence
on the melt rheological behavior of the PA6.
In tr od u ction
resulting terminal groups are either carboxylic acids or
amines. Since the nature of the terminal groups deter-
mines to a large extent the material as well as the
solution properties of dendritic polymers, we need for
an adequate comparison perfect dendritic aliphatic-
aromatic structures having not only identical repeating
units but also the same end groups as our phenol-
terminated hyperbranched poly(ether amide)s. For this
reason, the dendrimers were synthesized by nucleophilic
ring-opening addition reaction of phenols toward oxazo-
lines, which followed the same synthetic approach as
used for the synthesis of our previously27 described
hyperbranched poly(ether amide)s. This allows us to
prepare exact dendritic analogues to our hyperbranched
molecules and will contribute significantly to the struc-
ture property relationship studies in branched molecules
as it was started by Fre´chet et al.29 when he compared
structural identical linear, hyperbranched, and dendritic
polyesters.
Dendritic polymers, both the perfectly branched den-
drimers and the less perfect hyperbranched molecules,
have attracted much attention over the past decade.1,2
Amide junctions within the dendritic structure are often
used, starting with the very well-known aliphatic
PAMAM dendrimers reported by Tomalia,3 up to ali-
phatic-aromatic and fully aromatic amide dendrimers4,8
and several hyperbranched polyamides.9-14 Whereas for
example the PAMAM dendrimers found application in
pharmaceuticals15-20 and gene therapy,21-23 hyper-
branched polyamides have been discussed as blends
components in combination with linear polymers24 or
as additives and processing aids.25,26
In preceding work27 we reported the synthesis and
modification of hyperbranched aliphatic-aromatic poly-
(ether amide)s based on oxazoline chemistry with
phenolic end groups. We investigated their thermal and
rheological properties for potential application as a
rheological modifier in linear polyamide 6.25,26 As ex-
pected for hyperbranched polymers, an imperfect
branched structure and a broad molar mass distribution
were achieved; thus, analysis of the exact molar mass
of these highly branched poly(ether amide)s by size
exclusion chromatography (SEC) was difficult.28 Simi-
larly, exact correlation of structure/molar mass and the
properties of these molecules was not possible. There-
fore, we were interested in studying analogous perfectly
branched poly(ether amide) dendrimers to compare the
properties. Aromatic-aliphatic poly(ether amide) den-
drimers are known from the literature;4-7 however,
since all of them were synthesized by a convergent
approach via amidation using activation methods and
protective group techniques of peptide synthesis, the
The synthesis and modification of polymers using the
2-oxazoline group has been intensively studied for
several years.30,31 Beside the cationic ring-opening po-
lymerization using alkylation reagents as initiators,30,32
the ring-opening addition reactions of oxazolines with
thiol, phenol, or carboxylic acid groups to generate
thioetheramides, etheramides, or esteramides were
explored.33-35 These reactions can be used to enhance
molar mass by chain extension of polycondensates, to
cross-link, or to prepare linear polymers.33,36-40
Exp er im en ta l P a r t
Ma ter ia ls. All substances were used as purchased from
Aldrich, Fluka, or Merck in >99% purity (p.a.) quality without
further purification. All reactions were carried out under an
argon atmosphere. 2-(3,5-Dihydroxyphenyl)-1,3-oxazoline (3)
was prepared from N-(2-hydroxyethyl)-3,5-dihydroxybenz-
amide (2) as described previously.27 The linear PA6 supplied
by BASF AG, which was used as a matrix polymer, had a
* Corresponding author: Fax +49 (0) 351-4658-565, e-mail
voit@ipfdd.de.
10.1021/ma034318y CCC: $25.00 © 2003 American Chemical Society
Published on Web 08/29/2003

7066 Clausnitzer et al.
Macromolecules, Vol. 36, No. 19, 2003
molar mass of Mh w ) 76 000 g/mol (Mh n ) 17 400 g/mol) as
determined by SEC performed in hexafluoro-2-propanol +
0.05% trifluoroacetic acid potassium salt using a column
combination of Shodex HFIP precolumn, Shodex HFIP 803,
and Shodex HFIP 805 and calibration with poly(methyl
methacrylate) standards from Polymer Standard Services PSS
(0.5 mL/min, Kontron HPLC pump, detectors: UV photometer
GAT LCD 503 at 230 nm; differential refractometer ERC
7510). The relation of the end groups was 53 mmol/kg:57 mmol/
kg (COOH:NH2) which was determined by titration (data
supplied by BASF). The polyamide had a viscosity number
VN ) 149, measured with an Ubbelohde viscosimeter (Schott)
at 25 °C in 96% H2SO4 (VN ) (t1/t0 - 1)(1/c); t1, t0 ) flow times
of solution and solvent, c ) 0.005 g/mL of PA6 in sulfuric acid,
ISO307).
Blen d P r ep a r a tion . The blend preparation of polyamide
6 with dendrimers was carried out at 250 °C in a DACA twin-
screw microcompounder (DACA Instruments, model 20000)
with a mixing compartment volume of approximately 5 mL.
Both the matrix polymer PA6 and the dendrimer were added
as dry powders at the same time at a screw speed of 100 rpm,
and the components were mixed for 5 min. For comparison
reasons, the pure matrix PA6 was treated in the same way
before thermal and rheological analysis. The prepared mix-
tures contained an amount of 0.1 (P A6/GII-OH/01) and 1 wt
% (P A6/GII-OH/1) of the dendrimer GII-OH. All blends were
stored in a desiccator over silica gel after mixing to keep the
material dry.
Mea su r em en ts. Melting points were determined on a
Mettler FP 62 melting point instrument (scan rate 2 K/min)
and are uncorrected. The NMR spectra were recorded in 5 mm
o.d. sample tubes with a Bruker DRX 500 NMR spectrometer
at 500.13 MHz for 1H NMR spectra and at 125.75 MHz for
13C NMR spectra. DMSO-d6 was used as solvent for all NMR
experiments. For internal calibration the solvent peaks of
DMSO were used: δ (13C) ) 39.70 ppm, δ (1H) ) 2.5 ppm. The
signals were assigned by 1H-1H COSY and 1H-13C HMQC
techniques using the standard pulse sequences provided by
Bruker. FT-IR spectra were recorded with a Bruker IFS66V/s
spectrometer with a Golden Gate Unit (crystal: diamond,
single reflection, ATR technique). SEC measurements were
performed with a modular chromatographic KNAUER equip-
ment with an RI detector. A column set with two ZORBAX
columns PSM 60 and PSM 300 (silica microspheres 6 µm, mol
wt range 300-300 000 g/mol Rockland Technologies Inc.) was
used. The experiments were carried out at 25 °C in distilled
N,N-dimethylacetamide with 3 g/L LiCl and 2 vol % H2O
(calibrated with polystyrene (PS) or polyvinylpyridine (PVP)
standards, flow rate of 0.5 mL/min). The MALDI-TOF mass
spectra were recorded by a HP G2025A MALDI-TOF MS
system equipped with a N2 laser (337 nm) and a TLF unit. As
matrix materials were used 2,5-dihydroxybenzoic acid or
sinapinic acid (0.1 M THF solution) and Na+, Li+, or Cs+ as
modifier. The concentration of the sample solution was about
10-3 M. Mixtures of these solutions (10:1 matrix solution/
sample solution) were placed on the target and dried in a
vacuum.
The thermal behavior was investigated using a Perkin-
Elmer DSC 7 with Pyris-Software. The measurements were
carried out in aluminum pans under nitrogen in a temperature
range from -10 up to 250 °C with a scanning rate of (10
K/min as cycles consisting of first heating-cooling-second
heating scans. The glass transition temperatures were deter-
mined from the second heating run by the ∆cp half-step
method. The temperature and heat transitions were calibrated
with In and Pb standards. The melt rheological measurements
were performed using a Rheometrics ARES with plate-plate
geometry in oscillation mode under a nitrogen atmosphere at
250 °C. The plate diameter was 25 mm, and the gap ranged
from 0.6 to 1.3 mm. A frequency range between 0.1 and 100
rad/s and a strain within the linear viscoelastic range were
used. The blend samples were investigated as extruded strands
and the dendrimers as powders.
oxazoline (3) (4.41 g, 24.60 mmol), benzyl chloride (6.26 g, 49.40
mmol), dried potassium carbonate (8.51 g, 62.00 mmol), and
18-crown-6 (1.32 g, 5.00 mmol) in dry acetone was heated at
reflux and stirred vigorously under argon for 48 h. The mixture
was allowed to cool and was evaporated to dryness under
reduced pressure. The residue was partitioned between water
and CH2Cl2, and the aqueous layer was extracted three times
with CH2Cl2. The combined organic layers were then dried over
sodium sulfate, and the solvent was evaporated to dryness.
The crude product was purified by column chromatography,
eluting with ethyl acetate. The recrystallization from ethyl
acetate/hexane gave 4 as white crystalline solid: yield 60%;
mp 107.5 °C.
1H NMR: δ ) 7.42 (d, 4H, H10), 7.38 (t, 4H, H11), 7.32 (t,
2H, H12), 7.08 (d, 2H, H2), 6.84 (t, 1H, H4), 5.12 (s, 4H, H8)
4.37 (t, 2H, H7), 3.93 ppm (t, 2H, H6).
13C NMR: δ ) 162.82 (C5), 159.53 (C3), 136.90 (C9), 129.58
(C1), 128.57-127.73 (C10-C12), 106.76 (C2), 105.31 (C4), 69.61
(C8), 67.59 (C7), 54.50 ppm (C6).
FT-IR-ATR: ν ) 2970, 2900 (s, C-H), 1649 (w, CdN), 1594
(s, CdC), 1449 (m, C-H), 1165, 1059 cm-1 (s, C-O-C).
MALDI-TOF MS (5.96 µJ ): m/z ) 360 (M + H+), 382 (M +
Na+).
Gen er a l P r oced u r e for th e Rin g-Op en in g Ad d ition
Rea ction of P h en ol Gr ou p s tow a r d Oxa zolin e. Method
A. A mixture of the appropriate oxazoline (2 equiv) and N-(2-
hydroxyethyl)-3,5-dihydroxybenzamide (2) (1 equiv) was placed
into a Schlenk flask under argon. The flask was placed in an
oil bath preheated to 190 °C. The substances melted completely
after about 2 min, and the melt was stirred for 5 h at 190 °C.
After cooling, the crude product was purified as outlined in
the following text.
Method B. A mixture of the appropriate phenol and 2 equiv
per phenol group of 2-(3,5-bisbenzyloxyphenyl)-1,3-oxazoline
(4) was placed into a Schlenk flask under argon. The flask was
placed in a preheated oil bath. The substances melted com-
pletely after about 2 min, and the melt was stirred for 10 h at
appropriate temperature. After cooling, the crude product was
purified as outlined in the following text.
Gen er a l P r oced u r e for Clea va ge of th e Ben zyl Eth er s.
A solution of benzyl ether (1.00 mmol) in 10 mL of dry ethyl
acetate was added to a prehydrogenated suspension of 0.1 g
of dry 10% palladium-charcoal per available benzyl ether
protective group in dry methanol, and the mixture was stirred
vigorously at room temperature under hydrogen for 24 h. The
reaction mixture was then filtered through Celite and the
filtrate evaporated to dryness under reduced pressure. The
crude product was purified as outlined in the following text.
Con ver gen t Syn t h esis. HOCH2CH2NHCO-[G1]-(OBn)4
(G1a -Bn ): This compound was prepared from 2-(3,5-bisben-
zyloxyphenyl)-1,3-oxazoline (4) according to method A and
purified by column chromatography on silica gel eluting at first
with ethyl acetate to remove the byproducts. Subsequently,
ethyl acetate/methanol (5%) as eluent was used to give G1a -
Bn as white solid: yield 55%; mp 159.7 °C.
1H NMR: δ ) 8.65 (t, 2H, NH), 8.40 (t, 1H, NH), 7.44-7.30
(m, 20H, benzyl aryl-H), 7.13 (d, 4H, H12), 7.04 (d, 2H, H2),
6.82 (t, 2H, H14), 6.68 (t, 1H, H4), 5.11 (s, 8H, benzyl-CH2),
4.71 (t, 1H, OH), 4.13 (t, 4H, H8), 3.60 (q, 4H, H9), 3.47 (q, 2H,
H7), 3.28 ppm (q, 2H, H6).
13C NMR: δ ) 166.11 (C5), 165.83 (C10), 159.60 (C3), 159.56
(C13), 136.96 (Cbenzyl aryl), 136.86 (C1), 136.47 (C11), 128.63-
127.90 (Cbenzyl aryl), 106.51 (C12), 106.13 (C14), 104.87 (C2), 104.11
(C4), 69.70 (Cbenzyl-CH2), 66.41 (C8), 59.88 (C7), 42.39 (C6), 38.98
ppm (C9).
FT-IR-ATR: ν ) 3294 (br, N-H), 3064, 3033 (w, aryl-H),
2931, 2872 (s, C-H), 1630 (w, NHCdO), 1590, 1529 (s, CdC),
1437 (m, C-H), 1305 (s, O-H), 1163, 1058 cm-1 (s, C-O-C).
MALDI-TOF MS (2.83 µJ ): m/z ) 923 (M + Li+), 939
(M + Na+), 955 (M + K+).
HOCH2CH2NHCO-[G1]-(OH)4 (G1a -OH): This compound
was prepared from HOCH2CH2NHCO-[G1]-(OBn)4 (G1a -Bn )
following the general method for the benzyl ether cleavage.
The product was dried in a vacuum to give G1a -OH as white
solid: yield 89%; mp 140.9 °C.
Syn th esis of th e Mon om er . 2-(3,5-Bisbenzyloxyphenyl)-
1,3-oxazoline (4): A mixture of 2-(3,5-dihydroxyphenyl)-1,3-

Macromolecules, Vol. 36, No. 19, 2003
Poly(ether amide) Dendrimers 7067
1H NMR: δ ) 9.44 (s, 4H, OH), 8.38 (t, 3H, NH), 7.02 (d,
2H, H2), 6.67 (d, 4H, H,12 1H, H4), 6.33 (t, 2H, H14), 4.67 (t,
1H, OH), 4.10 (t, 4H, H8), 3.56 (q, 4H, H9), 3.48 (q, 2H, H7),
3.29 ppm (q, 2H, H6).
13C NMR: δ ) 166.93 (C10), 165.83 (C5), 159.57 (C3), 158.44
(C13), 136.82 (C1), 136.63 (C11), 106.09 (C2), 105.58 (C12), 105.31
(C14), 104.06 (C4), 66.38 (C8), 59.86 (C7), 42.36 (C6), 38.86 ppm
(C9).
FT-IR-ATR: ν ) 3381 (br, N-H), 3231 (br, O-H), 2942 (s,
C-H), 1710 (w, NHCdO), 1588, 1544 (s, CdC), 1444 (m, C-H),
1330 (s, C-O), 1160, 1065 (s, C-O-C),1005 cm-1 (s, C-OH).
MALDI-TOF MS (4,05 µJ ): m/z ) 556 (M + H+), 562 (M +
Li+), 578 (M + Na+).
Ox-[G1]-(OBn)4 (G1Ox-Bn ): G1a -Bn (0.50 g, 0.55 mmol)
was suspended in 2 mL of methylene chloride and cooled to 0
°C. Then thionyl chloride (0.1 mL, 1.3 mmol) was added
dropwise under stirring. After an additional 1.5 h, the ice bath
was removed and the solution was stirred at room temperature
until gas development was completed. The solution was poured
into ice water, and the organic layer was separated. The
organic layer was washed with sodium hydrogen carbonate
solution and water, dried over Na2SO4, and evaporated under
reduced pressure. The crude product was purified by column
chromatography on silica gel eluting with ethyl acetate to give
mainly the chloroethyl derivate (besides a small amount of
G1Ox-Bn ). The chloroethyl derivate reacts with KOH to the
oxazoline: KOH (0.043 g, 0.770 mmol) and 2-chloroethyl
derivate (0.24 g) were dissolved in consecutive order in 3 mL
of methanol and then refluxed for 1.5 h. After cooling the
solution was put into water, and the resulting suspension was
neutralized with aqueous acetic acid and filtered. The solid
was dried in a vacuum to give G1Ox-Bn : yield 51%; mp
146 °C.
1H NMR: δ ) 8.59 (t, 2H, NH), 7.43-7.30 (m, 20H, benzyl
aryl-H), 7.11 (d, 4H, H12), 7.00 (d, 2H, H2), 6.81 (t, 2H, H14),
6.72 (t, 1H, H4), 5.11 (s, 8H, benzyl-CH2), 4.34 (t, 2H, H7),
4.13 (t, 4H, H8), 3.91 (t, 2H, H6), 3.59 ppm (q, 4H, H9).
13C NMR: δ ) 166.09 (C10), 162.80 (C5), 159.69 (C3), 159.50
(C13), 136.92 (Cbenzyl aryl), 136.49 (C11), 129.58 (C1), 128.56-
127.82 (Cbenzyl aryl), 106.56 (C2), 106.51 (C12), 104.83 (C14), 104.53
(C4), 69.67 (Cbenzyl-CH2), 67.57 (C7), 66.42 (C8), 54.51 (C6), 39.03
ppm (C9).
FT-IR-ATR: ν ) 3295 (br, N-H), 3095, 3059 (w, aryl-H),
2987, 2901 (s, C-H), 1636 (w, NHCdO), 1592 (s, CdC), 1542
(s, CdC),1438 (m, C-H), 1157, 1059 cm-1 (s, C-O-C).
MALDI-TOF MS (4.28 µJ ): m/z ) 899 (M + H+), 921 (M +
Na+), 937 (M + K+).
HOCH2CH2NHCO-[G2]-(OBn)8 (G2a -Bn ): This compound
was prepared from Ox-[G1]-(OBn)4 (G1Ox-Bn ) according to
method A and purified by column chromatography on silica
gel eluting with methylene chloride/methanol (5%) for several
times. However, it was not possible to receive the product G2a -
Bn absolutely pure.
Diver gen t Syn th esis. MeO2C-[G1]-(OBn)4 (G1-Bn ): This
compound was prepared from methyl-3,5-dihydroxybenzoate
(1) according to method B at 160 °C and purified by column
chromatography on silica gel eluting at first with ethyl acetate
to remove the excess of 4. Subsequently, chloroform/ethanol
(1%) as eluent was used several times to give G1-Bn as white
solid: yield 51%; mp 160.4 °C.
1H NMR: δ ) 8.60 (t, 2H, NH), 7.43-7.30 (m, 20H, benzyl
aryl-H), 7.11 (d, 4H, H11), 7.08 (d, 2H, H2), 6.83 (t, 1H, H4),
6.81 (t, 2H, H13), 5.11 (s, 8H, benzyl-CH2), 4.15 (t, 4H, H7),
3.80 (s, 3H, H6), 3.60 ppm (q, 4H, H8).
MeO2C-[G1]-(OH)4 (G1-OH): This compound was prepared
from MeO2C-[G1]-(OBn)4 (G1-Bn ) following the general method
for the benzyl ether cleavage. The crude product was purified
by column chromatography on silica gel eluting with ethyl
acetate/methanol (1%) and dried in a vacuum to give G1-OH
as white solid: yield 98%; mp 194.7 °C.
1H NMR: δ ) 9.40 (s, 4H, OH), 8.38 (t, 2H, NH), 7.01 (d,
2H, H2), 6.82 (t, 1H, H4), 6.67 (d, 4H, H11), 6.34 (t, 2H, H13),
4.13 (t, 4H, H7), 3.82 (s, 3H, H6), 3.56 ppm (q, 4H, H8)
13C NMR: δ ) 166.93 (C9), 165.97 (C5), 159.84 (C3), 158.38
(C12), 136.66 (C10), 131.79 (C1), 107.79 (C13), 106.27 (C4), 105.62
(C11), 105.28 (C2), 66.55 (C7), 52.41 (C6), 38.83 ppm (C8).
FT-IR-ATR: ν ) 3381 (br, N-H), 3253 (br, O-H), 3088,
(w, aryl-H), 2924, 2854 (s, C-H), 1697 (s, ROCdO), 1643 (w,
NHCdO), 1589, 1541 (s, CdC), 1441 (m, C-H), 1344 (s, C-O),
1305 (s, O-H), 1158, 1061 (s, C-O-C), 1005 cm-1 (s, C-OH).
MALDI-TOF MS (2.70 µJ ): m/z ) 527 (M + H+), 549 (M +
Na+), 565 (M + K+).
MeO2C-[G2]-(OBn)8 (G2-Bn ). This compound was prepared
from MeO2C-[G1]-(OH)4 (G1-OH) according to method B at
180 °C and purified by column chromatography on silica gel
eluting at first with ethyl acetate to remove the excess of 4.
Subsequently, chloroform/ethanol (1%) as eluent was used
several times to give G2-Bn as colorless glass: yield 57%; Tg
73 °C.
1H NMR: δ ) 8.61 (t, 6H, NH), 7.42-7.28 (m, 40H, benzyl
aryl-H), 7.12 (d, 8H, H18), 7.06 (d, 2H, H2), 7.05 (d, 4H, H11),
6.81 (t, 5H, H,4 H20), 6.69 (t, 2H, H13), 5.10 (s, 16H, benzyl-
CH2), 4.12 (t, 12H, H,7 H14), 3.77 (s, 3H, H6), 3.59 ppm (q, 12H,
H,8 H15).
13C NMR: δ ) 166.07 (C16), 166.02 (C,5 C9), 159.60 (C3),
159.50 (C,12 C19), 136.90 (Cbenzyl aryl), 136.44 (C,10 C17), 132.29
(C1), 128.54-127.79 (Cbenzyl aryl), 106.50 (C,11 C18), 106.45 (C4),
106.19 (C,13 C20), 104.83 (C2), 69.56 (Cbenzyl-CH2), 66.40 (C,7 C14),
52.27 (C6), 39.03 ppm (C,8 C15).
FT-IR-ATR: ν ) 3325 (br, N-H), 3065, 3033 (w, aryl-H)),
2943, 2880 (s, C-H), 1719 (s, ROCdO), 1645 (w, NHCdO),
1590, 1529 (s, CdC), 1439 (m, C-H), 1342, 1300 (s, C-O),
1155, 1055 cm-1 (s, C-O-C).
MALDI-TOF MS (3.75 µJ ): m/z ) 1965 (M + H+), 1987
(M + Na+), 2003 (M + K+).
MeO2C-[G2]-(OH)8 (G2-OH): This compound was prepared
from MeO2C-[G2]-(OBn)8 (G2-Bn ) following the general method
for benzyl ether cleavage. The crude product was purified by
column chromatography on silica gel eluting with ethyl
acetate/methanol (20%) and dried in a vacuum to give G2-
OH as colorless glass: yield 83%; Tg 140 °C.
1H NMR: δ ) 9.44 (s, 8H, OH), 8.65 (t, 2H, NH), 8.42 (t,
4H, NH), 7.06 (d, 2H, H2), 7.03 (d, 4H, H11), 6.82 (t, 1H, H4),
6.67 (d, 10H, H,13 H18), 6.33 (t, 4H, H20), 4.13 (t, 4H, H7), 4.10
(t, 8H, H14), 3.80 (s, 3H, H6), 3.58 (q, 4H, H8), 3.55 ppm (q, 8H,
H15).
13C NMR: δ ) 166.91 (C,5 C,9 C16), 159.62 (C3), 158.38 (C,12
C19), 136.64 (C,17 C10), 136.42 (C1), 106.14 (C13), 106.27 (C,4 C13),
105.60 (C,18 C20), 105.28 (C2, C11), 66.50 (C7), 66.40 (C14), 52.39
(C6), 38.97 (C8), 38.87 ppm (C15).
FT-IR-ATR: ν ) 3254 (br, O-H, N-H), 2952 (s, C-H),
1705 (s, ROCdO), 1641 (w, NHCdO), 1587, 1539 (s, CdC),
1444 (m, C-H), 1340 (s, C-O), 1302 (s, O-H), 1160, 1061 (s,
C-O-C), 1005 cm-1 (s, C-OH).
MALDI-TOF MS (3.90 µJ ): m/z ) 1244 (M + H+), 1250
(M + Li+), 1266 (M + Na+).
MeO2C-[G3]-(OBn)16 (G3-Bn ): This compound was prepared
from MeO2C-[G2]-(OH)8 (G2-OH) according to method B at
190 °C. After cooling, the melt was stirred with methanol for
some hours to dissolve the excess of monomer 4. The crude
product was filtered off and purified by column chromatogra-
phy on silica gel eluting with chloroform/ethanol (3%) several
times to give G3-Bn as colorless glass: yield 32%.
1H NMR: δ ) 8.63 (t, 14H, NH), 7.40-7.27 (m, 80H, benzyl
aryl-H), 7.10 (d, 16H, H25), 7.04 (d, 14H, H2, H,11 H18), 6.79
(t, 9H, H,4 H27), 6.67 (t, 6H, H,13 H20), 5.07 (s, 32H, benzyl-
CH2), 4.09 (t, 28H, H,7 H,14 H21), 3.58 ppm (q, 28H, H,8 H,15
H22); H6 could not be detected.
13C NMR: δ ) 166.10 (C,5 C9), 159.84 (C3), 159.51 (C12),
136.92 (Cbenzyl aryl), 136.47 (C10), 131.79 (C1), 128.57-127.82
(Cbenzyl aryl), 107.86 (C13), 106.52 (C11), 106.32 (C4), 104.83 (C2),
69.68 (Cbenzyl-CH2), 66.57 (C7), 52.39 (C6), 39.01 ppm (C8).
FT-IR-ATR: ν ) 3321 (br, N-H), 3065, 3032 (w, aryl-H),
2944, 2879 (s, C-H), 1717 (s, ROCdO), 1640 (w, NHCdO),
1588, 1522 (s, CdC), 1437 (m, C-H), 1344, 1299 (s, C-O),
1157, 1053 cm-1 (s, C-O-C).
MALDI-TOF MS (2.35 µJ ): m/z ) 888 (M + H+), 910 (M +
Na+), 926 (M + K+)

7068 Clausnitzer et al.
Macromolecules, Vol. 36, No. 19, 2003
13C NMR: δ ) 166.07 (C,9 C,16 C23), 159.60 (C26), 159.49 (C3,
C,12 C19), 136.88 (C,10 C,17 C24), 136.43 (Cbenzyl aryl), 128.52-
127.77 (Cbenzyl aryl), 106.50 (C,11 C,18 C25), 106.19 (C,4 C,13 C,20
C27), 104.83 (C2), 69.64 (Cbenzyl-CH2), 66.40 (C,7 C,14 C21), 39.03
ppm (C,8 C,15 C22); C1, C5, and C6 could not be detected.
FT-IR-ATR: ν ) 3279 (br, N-H), 2933 (s, C-H), 1719 (s,
ROCdO), 1639 (w, NHCdO), 1589, 1526 (s, CdC), 1437 (m,
C-H), 1299 (s, C-O), 1155, 1054 cm-1 (s, C-O-C).
MALDI-TOF MS (6.94 µJ ): m/z ) 4119 (M + H+), 4455
(M + 337 (monomer 4)).
105.58 (C18), 105.30 (C20), 104.15 (C13), 94.28 (C2), 66.40 (C14),
66.11 (C7), 39.0 (C8), 38.87 ppm (C15).
MALDI-TOF MS (4.02 µJ ): m/z ) 1746 (M + Li+).
Cou p lin g of Den d r on s. C(O2C-[G1]-(OBn)4)2 (DG1-Bn ):
A mixture of MeO2C-[G1]-(OBn)4 (G1-Bn ) (0.60 g, 0.68 mmol),
1,4-bis(hydroxymethyl)benzene (6) (23.30 mg, 0.17 mmol), and
di-n-butyltin oxide (20.00 mg, 0.08 mmol) was put into a
Schlenk flask under argon. The flask was placed in an oil bath
preheated to 180 °C. The substances melted completely after
about 2 min, and the melt was stirred for 5 h at 180 °C. After
cooling, the crude product was purified by column chromatog-
raphy on silica gel eluting with chloroform to give DG1-Bn
as white solid: yield 67%; mp 85.2 °C.
[G1]-(OBn)6 (GI-Bn ): This compound was prepared from
phloroglucinol (5) according to method B at 200 °C and purified
by column chromatography on silica gel eluting at first with
ethyl acetate to remove the excess of 4. Subsequently, chlo-
roform/ethanol (1%) as eluent was used for several times to
give GI-Bn as white solid: yield 61%; mp 150.4 °C.
1H NMR: δ ) 8.58 (t, 3H, NH), 7.43-7.30 (m, 30H, benzyl
aryl-H), 7.12 (d, 6H, H11), 6.81 (t, 3H, H13), 6.16 (s, 3H, H2),
5.10 (s, 12H, benzyl-CH2), 4.06 (t, 6H, H7), 3.56 ppm (q, 6H,
H8).
1H NMR: δ ) 8.59 (t, 4H, NH), 7.43-7.28 (m, 20H, benzyl
aryl-H; 4H, H6′), 7.11 (d, 8H, H11), 7.08 (d, 4H, H2), 6.84
(t, 2H H4), 6.81 (t, 4H, H13), 5.29 (s, 4H, H6), 5.09 (s, 16H,
benzyl-CH2), 4.14 (t, 8H, H7), 3.59 ppm (q, 8H, H8).
13C NMR: δ ) 166.08 (C9), 165.27 (C5), 159.87 (C3), 159.49
(C12), 136.90 (Cbenzyl aryl), 136.44 (C10), 136.08 (C6′′), 131.68 (C1),
128.57-127.82 (Cbenzyl aryl), 128.23 (C6′′), 108.01 (C13), 106.51
(C11), 106.20 (C4), 104.82 (C2), 69.66 (Cbenzyl-CH2), 66.60 (C7),
66.18 (C3), 39.99 ppm (C8).
13C NMR: δ ) 166.06 (C9), 160.46 (C1), 159.51 (C12), 136.92
(Cbenzyl aryl), 136.48 (C10), 128.56-127.81 (Cbenzyl aryl), 106.52 (C11),
104.83 (C13), 94.33 (C2), 69.68 (Cbenzyl-CH2), 66.14 (C7), 39.02
ppm (C8).
FT-IR-ATR: ν ) 3269 (br, N-H), 3065, 3033 (w, aryl-H),
2940, 2873 (s, C-H), 1713 (s, ROCdO), 1642 (w, NHCdO),
1590, 1522 (s, CdC), 1441 (m, C-H), 1300 (s, C-O), 1153, 1055
cm-1 (s, C-O-C).
FT-IR-ATR: ν ) 3391 (br, N-H), 3064, 3032 (w, aryl-H),
2936, 2873 (s, C-H), 1638 (w, NHCdO), 1586, 1520 (s, CdC),
1438 (m, C-H), 1152, 1054 cm-1 (s, C-O-C).
MALDI-TOF MS (2.27 µJ ): m/z ) 1849 (M + H+), 1871
MALDI-TOF MS (6.33 µJ ): m/z ) 1211 (M + Li+), 1227
(M + Na+).
(M + Na+).
C(O2C-[G2]-(OBn)8)2 (DG2-Bn ): A mixture of MeO2C-[G2]-
(OBn)8 (G2-Bn ) (1.34 g, 0.68 mmol), 1,4-bis(hydroxymethyl)-
benzene (6) (23.30 mg, 0.17 mmol), and di-n-butyltin oxide
(40.00 mg, 0.16 mmol) was placed into a Schlenk flask under
argon. The flask was placed in an oil bath preheated to
180 °C. The substances melted completely after about 2 min,
and the melt was stirred for 9 h at 180 °C. After cooling, the
crude product was purified by column chromatography on
silica gel eluting with chloroform/ethanol (2%) to give DG2-
Bn as colorless glass: yield 20%; Tg 77 °C.
1H NMR: δ ) 8.65 (t, 12H, NH), 7.43-7.28 (m, 80H, benzyl
aryl-H), 7.39 (4H, H6′′), 7.16 (d, 16H, H18), 7.11 (d, 4H, H2),
7.09 (d, 8H, H11), 6.84 (t, 8H H20), 6.83 (t, 2H, H4), 6.72 (t, 4H,
H13), 5.29 (s, 4H, H6), 5.10 (s, 32H, benzyl-CH2), 4.15 (t, 24H,
H,7 H14), 3.63 (q, 24H, H,8 H15).
13C NMR: δ ) 166.00 (C16), 165.96 (C9), 165.16 (C5), 159.72
(C3), 159.50 (C12), 159.40 (C19), 136.79 (Cbenzyl aryl), 136.34 (C,10
C17), 134.31 (C6′), 131.68 (C1), 128.42-127.68 (Cbenzyl aryl), 127.93
(C6′′), 107.85 (C2), 106.41 (C18), 106.10 (C11), 106.02 (C4), 104.72
(C20), 104.11 (C13), 69.56 (Cbenzyl-CH2), 66.46 (C7), 66.31 (C,14 C6),
38.95 (C15), 38.87 (C8).
FT-IR-ATR: ν ) 3290 (br, N-H), 3065, 3033 (w, aryl-H),
2940, 2873 (s, C-H), 1713, 1643 (w, NHCdO), 1590, 1522 (s,
CdC), 1441 (m, C-H), 1153, 1054 cm-1 (s, C-O-C).
MALDI-TOF MS (2.27 µJ ): m/z ) 4008 (M + Li+), 4027
(M + Na+).
[G1]-(OH)6 (GI-OH): This compound was prepared from
[G1]-(OBn)6 (GI-Bn ) following the general method for benzyl
ether cleavage. The crude product was dissolved in a small
amount of N,N-dimethylacetamide, precipitated into water,
filtered off, and dried in a vacuum to give GI-OH as white
solid: yield 84%; mp 160.3 °C.
1H NMR: δ ) 9.39 (s, 6H, OH), 8.36 (t, 3H, NH), 6.67 (d,
6H, H11), 6.34 (d, 3H, H13), 6.14 (s, 3H, H2), 4.03 (t, 6H, H7),
3.52 ppm (q, 6H, H8).
13C NMR: δ ) 166.88 (C5), 160.46 (C1), 158.38 (C12), 136.67
(C10), 105.62 (C11), 105.27 (C13), 94.26 (C2), 66.12 (C7), 38.85
ppm (C8).
FT-IR-ATR: ν ) 3286 (br, O-H, N-H), 2944 (s, C-H),
1698 (w, NHCdO), 1588, 1541 (s, CdC), 1451 (m, C-H), 1305
(s, O-H), 1156, 1069 (s, C-O-C), 1005 cm-1 (s, C-OH).
MALDI-TOF MS (4.43 µJ ): m/z ) 664 (M + H+), 670 (M +
Li+), 686 (M + Na+).
[G2]-(OBn)12 (GII-Bn ): This compound was prepared from
[G1]-(OH)6 (GI-OH) according to method B at 180 °C and
purified by column chromatography on silica gel eluting with
chloroform/ethanol (1%) for several times to give GII-Bn as
colorless glass: yield 85%; Tg 74 °C.
1H NMR: δ ) 8.64 (t, 9H, NH), 7.41-7.27 (m, 60H, benzyl
aryl-H), 7.12 (d, 12H, H18), 7.05 (d, 6H, H11), 6.81 (t, 6H, H20),
6.68 (t, 3H, H13) 6.13 (s, 3H, H2), 5.09 (s, 24H, benzyl-CH2),
4.12 (t, 12H, H14), 4.03 (t, 6H, H7), 3.59 (q, 12H, H15), 3.54
(q, 6H, H8).
Resu lts a n d Discu ssion
13C NMR: δ ) 166.31 (C16), 166.24 (C9), 160.64 (C1), 159.83
(C12), 159.74 (C19), 137.14 (Cbenzyl aryl), 136.67 (C,10 C17), 128.78-
128.03 (Cbenzyl aryl), 106.75 (C18), 106.42 (C11), 105.06 (C20),
104.42 (C13), 94.51 (C2), 69.89 (Cbenzyl-CH2), 66.64 (C14), 66.35
(C7), 39.28 (C15), 39.22 (C8).
Mon om er Syn th esis. The aim of this work was to
synthesize ether amide dendrimers via ring-opening
addition of phenol groups toward oxazolines as described
previously for hyperbranched poly(ether amide)s.27 Both
the convergent and the divergent growth approach are
possible with the same AB2 monomer 2-(3,5-dihydroxy-
phenyl)-1,3-oxazoline (3), but it is necessary to protect
the reactive phenol groups. For this we used the benzyl
ether protective group as described by Hawker and
Fre´chet41 for the synthesis of 3,5-bis(benzyloxy)benzyl
bromide since deprotection by catalytic hydrogenation
can be performed under specific and mild conditions.
The etherification was carried out with benzyl chloride
in dry acetone and K2CO3 as base in the presence of
18-crown-6 (Scheme 1) to yield the protected monomer
4.
MALDI-TOF MS (5.11 µJ ): m/z ) 2827 (M + Li+).
[G2]-(OH)12 (GII-OH): This compound was prepared from
[G2]-(OBn)12 (GII-Bn ) following the general method for benzyl
ether cleavage. The crude product was dissolved in a small
amount of N,N-dimethylacetamide, precipitated into water,
filtered off, and dried in a vacuum to give GII-OH as white
solid: yield 79%; Tg 149 °C.
1H NMR: δ ) 9.42 (s, 12H, OH), 8.61 (t, 3H, NH), 8.38
(t, 6H, NH), 7.03 (d, 6H, H11), 6.67 (d, 15H, H,13 H18), 6.34
(t, 6H, H20), 6.14 (s, 3H, H2), 4.10 (t, 12H, H14), 4.05 (t, 6H,
H7), 3.56 ppm (q, 18H, H,8 H15).
13C NMR: δ ) 166.93 (C16), 166.04 (C9), 160.42 (C1), 159.63
(C12), 158.41 (C19), 136,63 (C17), 136.43 (C10), 106.15 (C11),

Macromolecules, Vol. 36, No. 19, 2003
Poly(ether amide) Dendrimers 7069
Sch em e 1
methanol (5%) as eluent (Rf ) 0.15) gave G1a -Bn in
55% yield and high purity. The following ring formation
to oxazoline G1Ox-Bn was not possible in one step as
described for monomer 4. The reaction of G1a -Bn with
thionyl chloride gave first chloroethyl benzoic acid amide
10, which formed the oxazoline ring with KOH/metha-
nol. Reaction of G1Ox-Bn with the monomer unit 2, as
above, gave the second-generation G2a -Bn of ether
amide dendron with focal N-hydroxybenzamide group.
But it was not possible to fully purify G2a -Bn by column
chromatography. Therefore, the divergent growth ap-
proach was investigated in order to have a more
versatile approach to this ether amide system.
Sch em e 2
Diver gen t Gr owth Appr oach . The divergent growth
approach is based on a two-step ring-opening addition
reaction/hydrogenation procedure (Scheme 3). Starting
from methyl-3,5-dihydroxybenzoate (1) treated with an
excess of 4 at 190 °C gave the first generation of benzyl
protected dendron in 51% yield after purification by
column chromatography. Hydrogenation of G1-Bn gave
the desired phenol-terminated dendron G1-OH. Simi-
larly, benzyl-terminated second- and third-generation
G2-Bn and G3-Bn were prepared from the phenol-
terminated dendrons G1-OH and G2-OH. Please note
that the convergently prepared dendrons G1a -Bn and
G2a -Bn have nearly the identical structure as G1-Bn
and G2-Bn , just having a different focal unit. Up to the
second generation all dendrons are fully characterized
by 1H and 13C NMR spectroscopy. Only for the third
generation the focal methyl benzoate group was not
detected whereas the other structural characteristics
were as expected. In this third generation a growing
spherical shape and thus lower distances between the
functional groups could be the reason for a transami-
dation side reaction induced by the high reaction
temperature. Therefore, the exact structure of G3-Bn
could not be completely verified.
Con ver gen t Gr ow th Ap p r oa ch . The convergent
synthesis is based on a focal group that is able to form
the oxazoline unit. We used the known27 N-(2-hydroxy-
ethyl)-3,5-dihydroxybenzamide (2) as focal group to
react with 4 in a ring-opening addition reaction, forming
the first generation G1a -Bn in bulk at 190 °C (Scheme
2). The purification by column chromatography was
difficult since G1a -Bn shows limited solubility in sol-
vents like ethyl acetate or chloroform, and the focal
N-hydroxybenzamide group leads to a high polarity of
the compound. However, the mixture ethyl acetate/
Coupling of the benzylic-terminated dendritic frag-
ments via transesterification of the focal methyl ben-
zoate was examined with a variety of cores (pentaeryth-
Sch em e 3

7070 Clausnitzer et al.
Sch em e 4
Macromolecules, Vol. 36, No. 19, 2003
Ta ble 1. Th eor etica l Mola r Ma sses of th e P oly(eth er
a m id e) Den d r im er s Com p a r ed to th e Mola r Ma sses
Deter m in ed by MALDI-TOF MS a n d SEC
MALDI-
b
b
MMcalcd TOF MSa SECPS-Stand
SECPVP-Stand
(g/mol)
dendrimer (g/mol)
m/z
(g/mol)
G1a -Bn
G1a -OH
G1Ox-Bn
G1-Bn
G2-Bn
G3-Bn
G1-OH
G2-OH
DG1-Bn
DG2-Bn
GI-Bn
GII-Bn
GI-OH
916.03
555.54
898.02
917
556
899
1600
1600
1200
1100
3000
6650
1100
3300
2400
5200
1600
4000
1650
4400
1800
1800
1400
1300
3200
7450
1400
3400
3100
6100
1800
4900
1900
5200
887.01
888
1964.19
4134.72
526.49
1243.20
1848.07
4002.47
1204.38
2820.18
663.63
1965
4136c
527
1244
1849
4004
1205
2821
664
GII-OH
1738.69
1740
ritol, phloroglucinol (5), 1,4-bis(hydroxymethyl)benzene
(6)) using a variety of catalysts (pyridine,42 p-toluene-
sulfonic acid,42 dibutyltin oxide, and with boron tribro-
mide as described by Yazawa et al.43). But only the
coupling with the bifunctional core molecule 6 as shown
in Scheme 4 produced the dendrimers DG1-Bn and
DG2-Bn in good yields after purification by column
chromatography.
a
Matrix: 2,5-dihydroxybenzoic acid or sinapinic acid. b Solvent:
DMAc/H2O/LiCl, RI detector. c Additional peaks in SEC.
branched poly(ether amide) prepared in a one-pot reac-
tion from the monomer 327 (Scheme 1), we used the
divergently grown unprotected dendrimer GII-OH (Fig-
ure 2). The dendrimer exhibits identical chemical shifts
for the protons as the hyperbranched polymer, with the
exception of the signals for the linear units (9.66 ppm
for O-H, 8.56 ppm for N-H, 6.9 and 6.5 ppm for
aromatic protons) which are only present in the hyper-
branched molecule and an additional signal at 6.14 ppm
for the core unit. The interior part of the dendrimer
corresponds to the dendritic unit and the exterior part
to the terminal unit of the hyperbranched polymer.
To obtain dendrimers with a trifunctional core, the
divergent growth synthesis starting from the trifunc-
tional phloroglucinol (5) core molecule as shown in
Scheme 5 was explored. A similar set of reaction steps
(ring-opening addition reaction/hydrogenation) as de-
scribed above was used to synthesize the first (GI-Bn ,
GI-OH) and second (GII-Bn , GII-OH) generation.
Ch a r a cter iza tion : NMR Sp ectr oscop y. The struc-
tures of all described compounds were fully established
1
by H and 13C NMR spectroscopy. The signals in the
SEC a n d MALDI-TOF MS. Table 1 shows the
results of MALDI-TOF MS and SEC of our dendrons
and dendrimers in comparison with the calculated
theoretical molar masses. Polystyrene (PS) and polyvi-
nylpyridine (PVP) were used for SEC calibration. The
results show that it is not possible to achieve the correct
molar masses for dendritic molecules using linear
standards as described also by Lederer et al.28 for the
analogous hyperbranched poly(ether amide)s. For hy-
perbranched polymers with molar masses higher than
10 000 g/mol, we obtained SEC molar mass values that
were much lower than those obtained by, for example,
light scattering methods. We explain this fact with the
different solubility and solvation behavior of the linear
standard and the hyperbranched polymer in the em-
ployed solvent N,N-dimethylacetamide. The dense globu-
lar structure of the hyperbranched polymers leads to
smaller molecule dimensions compared with the loosely
coiled linear standard molecules, and thus apparent
1H NMR spectra start to broaden significantly at the
third-generation dendrimer G3-Bn . Figure 1 shows the
1H NMR spectra of the second generation of the mono-
dendron G2-Bn , the coupled monodendron DG2-Bn ,
and the divergently grown dendrimer GII-Bn . All
spectra show characteristic signals of the poly(ether
amide) dendrimers, like for the aliphatic amide group
at 8.61 ppm and for the aliphatic CH2 groups at 4.1 and
3.6 ppm. Further characteristic chemical shifts were
observed for the protons of the benzylic protective group
at 5.1 and 7.3-7.43 ppm and for the protons of the core
unit of DG2-Bn (H6 and H6′′) and GII-Bn (H2). Ad-
ditionally, it is possible to distinguish the aromatic
protons of the dendritic unit (7.07 ppm for H11 and 6.7
ppm for H13) from the ones of the terminal unit (7.14
ppm for H18 and 6.82 ppm for H20).
To compare the proton spectrum of a perfectly
branched ether amide dendrimer with that of a hyper-
Sch em e 5

Macromolecules, Vol. 36, No. 19, 2003
Poly(ether amide) Dendrimers 7071
F igu r e 1. 1H NMR spectra of G2-Bn , DG2-Bn , and GII-Bn .
lower molar masses were calculated. But in the case of
the first- and second-generation dendrimers, we ob-
tained molar masses determined by SEC that were
higher than the calculated ones. This observation could
be explained by assuming that low-generation dendri-
mers have more an open fractal than a dense collapsed
structure with a strong influence of the functional
terminal units on the solvation behavior. A dense,
compact structure is reported mainly for dendrimers at
or above generation 4.2 In our case, on average the SEC
molar masses Mn of the dendrimers are 2 times higher
than the molar masses determined by MALDI-TOF MS
or the calculated ones. With increasing molar masses
of dendrimers the differences between SEC and MALDI-
TOF MS decrease. Also, because of the polar end-group
effect, the differences in molar masses of protected and
unprotected dendrimers are not represented in the SEC
values. MALDI-TOF mass spectrometry, however,
proved nicely the existence of the attempted dendrimers
and also the purity of the samples. Figure 3 shows a
series of MALDI-TOF MS spectra for GI-Bn , GI-OH,
G1-Bn , G1-OH, and G2-Bn . Only the different adducts
of the pure product with H, Li, and Na ions are shown
for GI-Bn and GI-OH (Figure 3a), whereas in G1-Bn ,
G1-OH, and G2-Bn (Figure 3b) small amounts of
impurities can be detected.
Differ en tia l Sca n n in g Ca lor im etr y. Differential
scanning calorimetric analysis revealed different ther-
mal transition for the dendritic molecules. All of the first
generation dendrimers melted between 100 and 160 °C
in the first heating. But it was not possible to recrystal-
lize the material (Figure 4), as observed also previously

7072 Clausnitzer et al.
Macromolecules, Vol. 36, No. 19, 2003
1
F igu r e 2. Comparison of H NMR spectra of dendrimer GII-OH and hyperbranched polymer P EA-OH.
Ta ble 2. Resu lts of DSC Mea su r em en ts
drimers in a linear matrix polymer. In previous work,
the effect of the hyperbranched P EA-OH on the melt
rheology and mechanical properties of polyamide 6 was
intensively studied.25 Would dendrimers show the same
influence to the flow properties of linear polyamide 6
as the hyperbranched analogue?
Tm (first heat), °C
Tg (second heat), °C
compound
R ) Bn
R ) OH
R ) Bn
R ) OH
G1a -R
G1-R
G2-R
DG1-R
DG2-R
GI-R
158
160
a
136
165
a
56
47
73
61
77
54
74
127
110
140
First, the melt rheological behavior of the pure ester
amide dendrimer was studied. For this, melt rheological
86
a
137
a
109
a
105
149
measurements (frequency sweep) on GII-OH (Mn
)
GII-R
1738 g/mol) were performed at 250 °C. The dendrimer
was stable under these conditions and repeated mea-
surements resulted in identical curves. Figure 5 shows
the result. As expected for the low molar mass sample,
the melt viscosity of the sample was in a rather low
range compared to the linear polyamide sample (see also
Figure 5). However, the dendrimer shows an increase
of the melt viscosity at lower frequency as observed
previously25 for hyperbranched polymers of identical
chemical structure. This indicates a predominately
elastic behavior of the sample as bulk material which
has been related to the polar end groups and their
possibility to form hydrogen bonds within the polymer
chain as well as toward other polymer chains resem-
bling a polymer network.
a
No melting.
for other poly(ether amide) dendrimers6 and by New-
come et al.44 for polyamide cascade dendrimers.
Two trends could be observed for the glass transition
temperatures comparing dendrimers of increasing gen-
eration and with different terminal groups (Table 2).
The Tg of all benzylic-terminated first-generation den-
drimers (G1a -Bn , G1-Bn , DG1-Bn , GI-Bn ) range from
47 to 61 °C, increasing with the molar mass. The Tg of
the analogous hydroxy-terminated dendrimers (G1a -
OH, G1-OH, DG1-OH, GI-OH) are approximately
twice as high due to the increased number of possible
hydrogen bonds. Up to the third generation the Tg
increases with the generation number, reaching 149 °C
for GII-OH. The literature45,46 describes higher genera-
tion dendrimers reaching a Tg plateau value. Compari-
son with the Tg of the analogous high molar mass
(Mn > 10 000 g/mol) hyperbranched poly(ether amide)
P EA-OH, which is between 150 and 160 °C, allows the
assumption that for the samples G2-OH and GII-OH
(Mn ) 1243/1738 g/mol; Tg ) 140 °C/149 °C) this plateau
value is almost reached.
The dendrimer sample GII-OH was also added in 0.1
and 1 wt % concentration to a linear polyamide 6 matrix
by melt mixing in a minicompounder. Similarly as the
hyperbranched samples, at this low amount the den-
drimer additive did not change the crystalline properties
of the polyamide matrix: Tc and Tm remained unef-
fected, and the corrected melt enthalpy even increased
slightly (Table 3). However, the glass transition tem-
perature Tg of the mixture increased considerably from
54 to 57 °C, indicating first a complete miscibility
between matrix polyamide and the dendrimer (only a
single Tg was observed) and second the preferential
incorporation of the dendritic additive in the amorphous
part of the polyamide 6. Using hyperbranched poly(ether
Melt Rh eology of Diver gen t Gr ow n Den d r im er
GII-OH. For having a direct comparison of the material
properties between hyperbranched polymers and den-
drimers, it was interesting to investigate their melt
rheological behavior as well as the effect of the den-

Macromolecules, Vol. 36, No. 19, 2003
Poly(ether amide) Dendrimers 7073
F igu r e 5. Plot of complex viscosity against frequency for
blends of PA6 and 0.1 and 1 wt % of GII-OH in comparison
with the pure blend components.
Ta ble 3. Th er m a l Tr a n sition s in Blen d s of P A6 a n d
Secon d -Gen er a tion Den d r im er GII-OH
a
b
c
d
e
f
Tc
(°C)
Tc,0
(°C)
∆Hc
(J /g)
Tm
(°C)
∆Hf
Tg
sample
(J /g) (°C)
P A6
188.8 192.3 -62.3 220.6 62.8
54
57
57
P A6/GII-OH/01 188.5 192.1 -65.1 220.6 67.6
P A6/GII-OH/1
189.1 192.6 -66.5 220.1 66.3
a
b
Crystallization temperature, peak maximum. Onset crystal-
lization temperature. c Heat of crystallization transition. Melting
d
temperature, peak maximum, second heat. e Heat of melting
transition, second heat, corrected for PA6 matrix content. f Glass
transition temperature.
low to observe an effect at this low concentration. For a
more detailed study, larger amounts of the dendrimers
are necessary as well as higher molar mass samples.
Nevertheless, it is noteworthy that the melt rheology
behavior of the plain dendrimer shows the same general
tendency as hyperbranched samples of identical struc-
ture with a strong interaction of the highly polar end
groups. Up to now only few melt rheology studies on
bulk dendrimers exist. But a complex viscosity-thinning
behavior dependent on shear rate, temperature, and
number of generations of poly(benzyl ether)47 and
PAMAM48 dendrimers in bulk was reported before
whereas in concentrated solution of dendrimers mainly
Newtonian behavior was observed.49
F igu r e 3. MALDI-TOF mass spectra of (a) GI-Bn and GI-
OH and (b) G1-OH, G1-Bn , and G2-Bn .
Con clu sion s
Aliphatic-aromatic poly(ether amide) dendrimers
were synthesized up to generation 3 via ring-opening
addition of phenol groups toward oxazoline in bulk
between 140 and 190 °C. The first and second genera-
tions were prepared in both convergent and divergent
approaches. The dendrons and dendrimers were char-
acterized by 1H and 13C NMR spectroscopy and MALDI-
TOF MS, and the purity and the perfect structure of
the products were verified, indicating that the addition
reaction is quite selective even at these high reaction
temperatures. The products were compared to chemi-
cally identical hyperbranched poly(ether amide)s pre-
pared in a one-step process from AB2 monomers. DSC
measurements indicated that the model dendrimers of
lower generation are still able to crystallize, but the
higher generations are amorphous with a Tg approach-
ing the values of the high molar mass hyperbranched
materials with identical end groups. Melt rheology
measurements on the dendrimers revealed a predomi-
nantly elastic behavior with a relatively high viscosity
at low frequency as found for the hyperbranched ana-
F igu r e 4. Plot of first and second heat of first- and second-
generation dendrons G1-Bn and G2-Bn .
amide)s,25 even this low content of a highly branched
additive resulted in a decrease of the melt viscosity of
the linear matrix. As shown in Figure 5, the dendrimer
sample had no effect on the matrix viscosity. However,
the hyperbranched polymer used before had a much
higher molar mass (Mn > 20 000 g/mol), and the effect
on melt viscosity was also lower when lower molar mass
hyperbranched samples had been used.26 Thus, we
assume that the molar mass of the dendrimer was too

7074 Clausnitzer et al.
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